Normal retinal ganglion cell (RGC) production and candidate disease associated genes identified in optic nerve hypoplasia (ONH)

Abstract

Purpose : Children with ONH (a leading cause of permanent congenital blindness) lack vision because they are born deficient in RGCs. Developmental events that underlie ONH and frequently associated neurologic and endocrine abnormalities are unknown. While likely a multifactorial disease with both environmental and genetic contributions, environmental influences are unclear and genetic underpinnings have not been well explored. To investigate the contribution of genetic factors, we sought to identify candidate causal genes through exome sequencing. Additionally, we developed an iPSC derived disease model that recapitulates retinal development to determine whether an ONH genetic background alters production or gene expression of RGCs.

Methods : Exome DNA was sequenced from genomic DNA of afflicted children and their parents. Inheritance modeling of rare variants restricted the data to that with potential for robust contribution to disease. RGCs with ONH and control genetic backgrounds were differentiated from iPSCs derived from blood of afflicted and healthy children. Flow cytometry was employed for RGC quantitation. For transcriptome analyses, RNA was isolated from RGCs, sequence obtained from NGS libraries, and DESeq2 used to determine differential expression between ONH and controls.

Results : In two rare, familial cases of mild ONH, with atypical phenotypes beyond neurologic or endocrinologic systems, deleterious variants in three candidate disease contributing genes were identified. Among variants in 42 genes that passed initial filtering criteria from 34 typical ONH patients, there is one strong candidate causal gene. No genes elucidated in this study match those with a previously reported ONH association. In iPSC-derived ONH and control retina (three genetic backgrounds each), RGC production was similar, but 16 significantly differentially expressed genes were detected.

Conclusions : The novel genes identified in atypical, familial ONH, along with 50 genes previously reported, implies that many genes can contribute to an ONH phenotype. That clear candidates for causing monogenic disease are rare in typical ONH suggests that genetic risk commonly arises from multiple genes. While genetic factors do not diminish RGC production in our iPSC models, the differentially expressed genes in ONH RGCs indicates that the disease population may share expression altering variants.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.